Often I hear the question “why high school” and this is a very valid question as so many of anime takes place in high school or feature high school aged characters. So here is my take on this question.
Please note that this is not about demographics as almost everyone in Japan has exposure to manga and anime, but they’ve been around the Western world for only a couple of decades. This is more of why rather than who.
The setting of high school allows for diversity of characters compared to the later years. Colleges are divided by somewhat similar majors, work place is divided by departments, and fantasy genre is divided by their own set of organization. In high school, you can have a jock and a nerd be in the same class. It is a melting pot of diversity.
Not everyone goes to college, and not many people go to college along with their friends. So in a sense, high school is the last chance where everyone from different parts of life are at one place doing something similar together. After this, everyone goes their separate ways.
Teenage years are seen as time of change, the chance to grow into a full fledged adult. And it just happens that these take place in high school
I think the high school setting in sports anime is really good. Think about it. Do you think such a great underdog story like Eyeshield 21 will happen in college or in the professional level? High school level sport makes it so that you can have a complete noob and a borderline professional be in the same tournament and/or team seem normal
Like sports, cooking is something that has huge range of skills from noobs to pros, and high school may be the ideal setting for this. It allows people from different backgrounds to compete on similar platform. Sure, Shokugeki no Soma might not be the best example as everyone there is an expert, but it is close as Soma comes from family restaurant while some of the other characters come from fancier places.
I also think romance set in high school setting makes sense. While puberty really starts in middle school, I think it is in high school where all the drama is pushed to dial 11. Sure there are a lot of romance that happens in college, just look at Genshiken, but they are more mature and refined. While high school is about not letting your crush know you have a crush on them. The story literally writes itself.
on the other hand, there are series or genres that stay with high school theme needlessly.
I think fantasy genre has so much potential in anime but it can be bogged down by the high school setting or high school age characters. I am talking about things like Shin Megami Tensei series, Fate/ Stay Night, Sword Art Online, etc. Let me explain.
Shin Megami Tensei, a series I love by the way, has a tradition of making characters from high school, and they love to stick to this rule. But why though? Being dropped in a post-apocalyptic world will be weird for anyone, not just teenagers. Hell, adults might have harder time adjusting to such drastic changes. And there has been SMT games with adult cast: Strange Journey, Persona 2, and Soul Hackers. For the Persona series, this makes a little more sense since they are more about discovering who they are as people rather than recreating the world in your image. I feel like the high school setting is there has a shackle rather than it making sense.
Fate/ Stay Night, another series I love to death, has similar problem, in that good chunk of the cast are high school students. It seems like kids fighting and killing each other. Take Fate/ Zero a look, it is a lot more mature simply by aging up the characters. Apart from Waver, everyone of the main cast is an adult. Sure kids can do nasty stuff to another human being, but adults can easily take this to whole new level. I still do love Fate/ Stay Night, but Fate/ Zero is fart more mature and more fitting to the its story than the original.
When I say Sword Art Online, I am kind of saying this as a stand in for the “Life in Another World” genre. SAO, No Game No Life, Re:Zero, Netoge Yome and KonoSuba all have teenagers as main focus. The only exceptions to this I can think of are GATE, Log Horizon, and kinda Youjo Senki. Here are where things get less clear. While the average age for gamers is around 30, most “adults” don’t play too much games. So the teenage cast does make sense. But the level of complexity an adult mind can bring to these are undeniable, just look at the political and legal system made in Log Horizon and the cruel indifference to life of Youjo Senki. That said, series like Re: Zero and NGNL does bring level of complexity with their more damaged and level headed main characters. So this sub-genre is more in gray area than the previous mentioned.
More popular Shonen series more or less avoid this in the fantasy genre by having a mixed age group with the main characters. One Piece has Nico Robin (28), Franky (34), and Brook (86) before the time skip. Naruto has Kakashi (26), Guy (26), and Jiraiya (50). Hell, Dragon Ball had kids, to teens, to adults. And this mix of age groups did allow for wider range of skill levels among the characters as well as wider appeal.
So am I saying that high school setting is great? Well, I guess I am saying it depends. Let me elaborate. I think the reason people ask this question is because the sheer number of this kind setting in manga and anime.
I hoe you like this little rant.